<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script type="text/javascript">
			function TreeNode(val, left, right) {
				this.val = (val === undefined ? 0 : val)
				this.left = (left === undefined ? null : left)
				this.right = (right === undefined ? null : right)
			}
			let r = new TreeNode(1,
				new TreeNode(2,
					new TreeNode(4, null, null),
					new TreeNode(5, null, null)),
				new TreeNode(3,
					new TreeNode(6, null, null),
					new TreeNode(7, null, null)));
			var inorderTraversal = function(root) {
			    const res = [];
			    const inorder = (root) => {
			        if (!root) {
			            return;
			        }
			        inorder(root.left);
			        res.push(root.val);
			        inorder(root.right);
			    }
			    inorder(root);
			    return res;
			};
			console.log(inorderTraversal(r));
		</script>
	</body>
</html>
